Nonwoven fabrics and their manufacture have been the subject of extensive development resulting in a wide variety of materials for numerous applications. For example, nonwovens of light basis weight and open structure are used in personal care items such as disposable diapers as liner fabrics that provide dry skin contact but readily transmit fluids to more absorbent materials which may also be nonwovens of a different composition and/or structure. Nonwovens of heavier weights may be designed with pore structures making them suitable for filtration, absorbent and barrier applications such as wrappers for items to be sterilized, wipers or protective garments for medical, veterinary or industrial uses. Even heavier weight nonwovens have been developed for recreational, agricultural and construction uses. These are but a few of the practically limitless examples of types of nonwovens and their uses that will be known to those skilled in the art who will also recognize that new nonwovens and uses are constantly being identified. There have also been developed different ways and equipment to make nonwovens having desired structures and compositions suitable for these uses. Examples of such processes include spunbonding, meltblowing, carding, and others which will be described in greater detail below. The present invention has general applicability to nonwovens as will be apparent to one skilled in the art, and it is not to be limited by reference or examples relating to specific nonwovens which are merely illustrative.
It is not always possible to efficiently produce a nonwoven having all the desired properties as formed, and it is frequently necessary to treat the nonwoven to improve or alter properties such as wettability by one or more fluids, repellency to one or more fluids, electrostatic characteristics, conductivity, and softness, to name just a few examples. Conventional treatments involve steps such as dipping the nonwoven in a treatment bath, coating or spraying the nonwoven with the treatment composition, and printing the nonwoven with the treatment composition. For cost and other reasons it is usually desired to use the minimum amount of treatment composition that will produce the desired effect with an acceptable degree of uniformity. It is known, for example, that the heat of an additional drying step to remove water applied with the treatment composition can deleteriously affect strength properties of the nonwoven as well as add cost to the process. It is, therefore, desired to provide an improved treatment process and/or composition for nonwovens that can efficiently and effectively apply the desired treatment without adversely affecting desirable nonwoven web physical properties and achieve the desired results.
It is also known that most conventional surfactants that are water dispersible are not prone to form high-solids (&gt;10 weight %), low viscosity (&lt;100 cp), stable mixtures with water. An additional desire, therefore, is to provide a high-solids treatment bath that is stable without phase separation over an extended period and that exhibits a low viscosity profile at room temperature as well as means to effectively apply the surfactant treatment to impart a durable hydrophilic character to the substrate such as a nonwoven.